Human coronaviruses cause 15 to 30 percent of common colds, yet there has been little investigation of these human pathogens. Our long term goal is to develop anti-viral drugs to prevent and/or treat human coronavirus infections of the upper respiratory tract. We anticipate that these drugs would be used in combination with drugs to prevent or treat colds due to rhinoviruses which are now being developed in other laboratories. By covering the viruses that cause most common colds, such combination drugs would make it unnecessary to identify the type of common cold virus causing early symptoms before initiating therapy. Our strategy for developing anti-coronavirus drugs is to use information about viral spike protein and receptor structure and function to identify small molecules that may block interactions of the viral spike glycoprotein with its cellular receptor glycoprotein. Our lab has identified receptors for human, murine and feline coronaviruses. We have expressed and purified soluble recombinant receptor glycoproteins, and are testing them for receptor activities. We will use mutagenesis to identify the amino acids and domains of the viral spike proteins and receptor glycoproteins that interact, and test the mutant proteins for binding activity and the ability to induce or undergo conformational changes that lead to membrane fusion and virus entry. We will analyze the structures of the spike proteins and receptor glycoproteins using cryo-electron microscopy and X-ray crystallography. The resulting structural models will be used to develop small molecules that block virus binding and/or receptor induced conformational changes in the spike protein. These molecules will be tested in cell culture model systems for toxicity and for the ability to block virus infection. Non-toxic drugs with anti-viral activity in cultures will be tested in animal model systems for the ability to block coronavirus infections of the respiratory tract. Our experimental models are the interactions of two coronaviruses, mouse hepatitis virus (MHV) and human coronavirus 229E (HCoV-229E), with their receptors, MHVR and hAPN, respectively. The murine model is more advanced than the human model, and will provide information and strategies that will facilitate our studies on human coronavirus-receptor interactions. The MHV model will also provide fundamental information on how an immunoglobulin-related receptor initiates infection with an enveloped virus. The 229E model will elucidate how the enzyme APN acts as a virus receptor. Inhibition of HCoV-229E respiratory infection by candidate drugs will be studied in transgenic mice that express the HCoV-229E receptor, hAPN, in the respiratory epithelium.